This invention pertains to a catalytic multistage process for hydrogenation and hydroconversion of heavy hydrocarbon feed materials by utilizing a highly-dispersed iron-based catalyst to produce lower-boiling hydrocarbon liquid fuel products. The invention pertains particularly to such catalytic multi-stage hydrogenation process utilizing an in-line catalytic hydrotreating step for feedstreams of coal, heavy petroleum residua, plastic wastes, and combinations thereof.
Coal hydrogenation and liquefaction processes using various iron-containing compounds such as pyrites (FeS.sub.2) and red mud (Fe.sub.2 O.sub.3) as catalysts have been well known for many years. Such particulate iron-containing catalyst compounds were usually added in small amounts to a coal-oil slurry feedstream upstream of a catalytic reactor operated at elevated temperature and pressure conditions. However, because of the generally low effectiveness of such known iron-based catalytic compounds, primarily due to their low initial surface areas and inability to provide high levels of dispersion under reaction conditions, catalytic hydroconversion processes for coal and heavy petroleum resid feedstocks which have been developed during the past 30 years have usually utilized a bed of particulate supported type catalysts in the reactors. Such supported catalysts may be beads or extrudates containing small amounts of one or more active promoter metals such as cobalt, molybdenum or nickel deposited on an inert support material such as alumina or silica. Such particulate supported catalysts are used in either downflow fixed bed type reactors or in upflow ebullated bed reactors maintained at desired reaction conditions of temperature, pressure and space velocity.
Although such particulate supported type catalysts such as cobalt-molybdenum or nickel-molybdenum deposited on alumina or silica supports and catalytic hydroconversion processes using the supported catalysts have provided generally good results for hydrogenation and hydroconversion of coal and heavy oil feed materials, some disadvantages of such particulate supported type catalysts are their relatively poor contact with the feed materials and their rapid deactivation caused by deposition on the catalyst of coke and metal contaminants such as iron, nickel, titanium and vanadium contained in the feeds. U.S. Pat. No. 4,136,013 to Moll et al discloses an emulsion type metal catalyst useful for hydrogenation processes, but it also has disadvantages of low catalytic activity and high catalyst usage. At the levels of catalyst usage disclosed in the Moll et al. patent, the catalyst cost becomes prohibitive unless the catalyst is recovered from the unconverted feed material and reused. U.S. Pat. Nos. 4,077,867 and 4,134,825 to Bearden et al. disclose an in-situ formed metal-carbon containing dispersed slurry catalyst called `M-Coke` for hydroconversion of coal, heavy oil, and mixtures thereof, and are primarily based on molybdenum which is significantly more expensive than iron. U.S. Pat. No. 4,486, 293 to Garg disclosed a co-catalyst combination of iron and Group VI or VIII non-ferrous metal for liquefaction of coal in hydrogen-donor solvent using water soluble salts of the co-catalyst metals.
It is known that catalysts formed from water-soluble precursor salts often undergo sintering under coal liquefaction conditions and lack the high degree of dispersion necessary for high catalytic activity. U.S. Pat. No. 4,895,821 to Kainer et al discloses a fine grained iron oxide catalyst composition produced by reacting the iron oxide with sulfuric and phosphoric acids. U.S. Pat. No. 5,168,088 to Utz et al. discloses a unique way of improving a slurry catalyst dispersed during coal liquefaction by precipitating the iron oxide onto the coal matrix. However, such precipitation of a catalyst on the entire coal feed would be difficult and very expensive for commercial scale operations. Thus, further improvements are needed in catalyst forms and compositions and also in processes for catalytic hydroprocessing of various carbonaceous feedstocks, particularly for utilizing dispersed iron-oxide based catalysts that are highly active, environmentally benign, and less expensive for the catalytic hydroconversion processes in which they are used.
In the improved process of this invention for catalytically and hydrogenating and hydroconverting heavy hydrocarbon feed material such as coal, the coal is pulverized and fed as a slurry containing a highly dispersed iron-based catalyst into a first-stage, back-mixed reactor together with hydrogen at appropriate high temperature and pressure conditions, and is reacted to break down the high molecular weight carbonaceous materials into lower molecular weight, lower sulfur, and lower boiling hydrocarbon distillates and gases. Prior processes for direct catalytic liquefaction of coal and heavy oils are significantly different, in that they use particulate supported type catalysts in either fixed bed type reactors or fluidized ebullated bed type reactor systems. Also, some prior coal hydrogenation processes are dependent on separate hydrogenation of the coal slurrying oil to provide a hydrogen donor solvent liquid in the reactor. But no known prior hydrogenation processes for heavy hydrocarbon feed materials contain the combination of process steps and maximization of catalyst activity and reactor kinetics provided by this invention.
It is known that carbonaceous material deposition occurs in coal liquefaction reactor systems that are not mechanically back-mixed and that ebullated bed type catalyst systems using particulate supported catalysts experience rapid catalyst aging and deactivation and are difficult to operate. However, this invention avoids such operational problems by the continuous addition of fresh highly dispersed iron-based gel or liquid type catalyst into two-staged reactors, which are utilized in combination with an in-line fixed bed catalytic hydrotreating reactor containing a supported type catalyst that hydrotreats light and medium boiling range distillate fractions from the prior catalytic liquefaction steps, so that the supported hydrotreating catalyst is not exposed to the heavy unconverted residuum and ash from the coal feed, and its resulting catalyst deactivation rate is minimal. Additionally, for lower rank, high-oxygen containing coals and in catalytic two-stage reactor processes without an interstage phase separation step, hydrogen is undesirably consumed by converting the oxygen in the feed to water, and in increased production of undesired light C.sub.1 -C.sub.3 gases in the second stage catalytic reactor. However, such disadvantages of the prior art processes have now been overcome by providing a catalytic multi-stage hydrogenation process having an interstage phase separation step, so that hydrogen consumption is reduced because the oxygen contained in the coal feed is removed as CO.sub.2, and the light distillates are removed for fixed bed catalytic hydrotreatment and molecular rearrangement at lower temperature. Furthermore, removal of light fractions in the interstage separation step improves kinetics in the second stage catalytic reactor by increasing the concentration of heavy oils and coal-derived liquids and hydrogen partial pressure entering the second stage reactor. Although some known coal liquefaction and oil hydrotreating technologies have incorporated in-line fixed-bed catalytic hydrotreating step, but none have provided the combination and process sequence utilized in the present invention for maximizing hydrogenation, molecular rearrangement, and heteratom removal for the most valuable distillate fractions produced in combination with dual back-mixed highly dispersed catalytic reactor systems. The production of clean, high quality liquid fuels from heavy hydrocarbon feed materials such as coal, petroleum, and plastic wastes at high efficiency by utilizing this invention could not be foreseen or expected from the known individual process steps.